1. Field of the Invention
This invention relates to a gas deposition apparatus, and more particularly to a gas deposition apparatus in which ultra fine particles are transported with an inert gas, and are ejected at a high speed from a nozzle onto a substrate positioned in direct facing relationship to the nozzle to form a thick film or condensate of the ultra fine particles on the substrate.
2. Description of the Prior Art
A new maskless film-making method using ultra fine particles has been established, named the gas deposition method. This method has the following characteristics compared with conventional methods: 1) Dry processing; 2) Direct write processing, maskless (50 .mu.m width); 3) High deposition rate processing (.sup..about. 100 .mu.m/sec), and 4) Low temperature processing (250.degree. C.).
Ultra fine particles (UFP) of organic and inorganic materials can be formed by the gas evaporation method (gas condensation method). In the gas deposition method, particles formed by the gas evaporation method in an evaporation chamber are carried to another chamber (the deposition chamber) through a pipe. Particles are accelerated in the pipe with a gas flow and come out of a nozzle located in the deposition chamber. This chamber is evacuated down to less than 10.sup.3 Pa, and the particles are deposited on a substrate to form UFP films. The speed of the particles as they exit the nozzle depends on the pressure difference between the evaporation chamber and the deposition chamber.
The particles speed exceeds 500 m/s and adhesion strengths of the films reach 20 kgf/mm.sup.2 which is comparable to electroplating films. This is achieved where the pressure of the evaporation chamber is at 2 atms, and the temperature of a Ni substrate is 200.degree. C. Patterns of spots and lines with 50 .mu.m size and also wider films can be formed on a substrate without a masking system. The deposition rate can exceed 100 .mu.m/sec using a nozzle with an inner diameter of 600 .mu.m.
Generally, ultra fine particles are formed by the gas evaporation method. In the gas evaporation method, metal atoms are evaporated in an inert gas such as helium or argon, collided with gas atoms and cooled, thereby condensing into particles. The particles sizes are controlled by changing the evaporation temperature or the gas pressure. Larger sized particles can be formed under the conditions of higher temperature or higher pressures.
The formed particles by the gas evaporation method are carried to another chamber through a pipe while in an aerosol state. The particles are accelerated in the pipe and sprayed on a substrate through a narrow nozzle and deposited on the substrate in the form of a UFP film. This method is called the gas deposition method. As for materials and forms of substrates, there are no restrictions; glass, ceramics, etc., can be used.
This method is expected to be used for forming electronic conductive films, resistive films, and dielectric films for hybrid microelectronics because it has several advantages over conventional methods including direct write processing, low temperature processing, and the ability to form uniformly mixed UFP films using more than two elements.
The schematic diagram of the gas deposition apparatus of the prior art is shown in FIG. 1. The gas deposition apparatus 1" is mainly composed of a UFP evaporation chamber 11, a deposition chamber (a spray chamber) 18, a transfer pipe 16, and a gas circulation system. The chambers to which pressure gauge 6 and 7 are attached, respectively, are evacuated down to 10.sup.-4 Pa, and then helium gas is supplied through a variable flow valve 3 from a bottle 2. The gas is carried to the deposition chamber 18 through the transfer pipe 16. The gas pressure of the evaporation chamber 11 is controlled from 1 atm to 4 atms by changing the helium gas supplying speed and the gas pumping speed.
Metal atoms are evaporated from a crucible which, for example, contains Au (gold). The crucible is resistance heated by an alternating current (AC) power source 13. Evaporated atoms colliding with gas atoms are cooled, condensing into particles.
In the case of Au film formation, the evaporation temperature is controlled at between 1500.degree. C. and 1700.degree. C. In the case of Ag film formation, the evaporation temperature is controlled at between 1300.degree. C. and 1500.degree. C. In the case of Cu and Pd film formation, the evaporation temperature is controlled at between 1450.degree. C. and 1550.degree. C., respectively.
The condensed particles are carried through the transfer pipe 16 with the gas flow as shown by the arrow. The particles carried through the transfer pipe 16 are ejected out of the nozzle 17 in the deposition chamber 18 and deposited on a substrate 19. The deposition chamber 18 is pumped down to less than 10.sup.3 Pa through a vacuum valve 4 by a pump system 5 of a mechanical booster pump and a rotary pump.
A substrate holder 9 is designed to be moved along the X direction as shown in FIG. 1, and in the Y direction and the Z direction making right angles with each other, by a digital programmable controller. The scanning speed of the substrate 19 is controlled between 0.01 mm/sec and 2 mm/sec.
Using the controller, a desired pattern of UFP can be formed on the substrate 19. When the substrate 19 is not moved, a pillared condensate of UFP is formed on the substrate 19.
The thick film formed by the gas deposition method consists only of Au, and so it has the advantage that it does not include a high polymer binder, in contrast to other prior art methods.
However, this gas deposition method of the prior art has still the following problems: Aggregates of ultra fine particles are apt to be included in the film, resulting in deterioration of film characteristics and lowering of adhesion strength between the film and the substrate. The nozzle is also sometimes clogged with aggregates. Furthermore, the time during which a good film can be stably obtained is short.